The present invention relates to a thermal head for use in a facsimile machine, a printer, a portable apparatus, and the like, and to a method of manufacturing the same.
FIG. 11 is a sectional view illustrating a structure of a conventional thermal head. Generally, in the conventional thermal head, a heater 2, an electrode 3, and a protective film 4 are formed on a plate-like substrate 7 made of glazed ceramic or the like, and a driver IC 5 whose terminals are connected to the electrode 3, and an encapsulation 6 for protecting the IC are provided thereon. The encapsulation 6 is prepared such that silicon resin, epoxy resin or the like is coated to the IC, and then is subjected to curing. Further, in FIG. 11, although the driver IC is mounted by wire bonding, there is also a case where the driver IC is mounted according to what is called the face-down method. The heater, the electrode, and the protective film on the thermal head substrate are formed by a thick film process, a thin film process, and a photolithographic process, which are all costly. Thus, usually, a plurality of thermal heads are laid out on a large wafer such that a plurality of thermal heads are manufactured simultaneously by processing one wafer. Since, as mentioned the above, the process is costly, in view of the manufacturing cost, it is desirable that as many as possible thermal heads as many as possible are laid out on a large wafer.
On the other hand, a facsimile machine, a printer, and the like, especially those used in the field of portable apparatus, are now being miniaturized and and the overall weight reduced. In view of the trend toward miniaturizing and reducing the weight of the apparatus, miniaturization of a thermal head for use in the apparatus is also required.
In the context mentioned above, in order to get a greater number of thermal heads from one wafer, a thermal head is required to be sized smaller with the limitations mentioned above.
Moreover, in a schematic sectional view of a driver IC mounting portion of a thermal head shown as shown in FIG. 12, a width 8 of the encapsulation 6 for protecting the IC has a smallest necessary value, i.e., the width 8 can not be made smaller than a width 9 of the IC. Further, since the encapsulation is carried out by coating and curing the resin, due to flowing out of the resin before curing shown by a dotted line in FIG. 12, the width of the encapsulation becomes wider than that at the time of coating.
A Therefore, conventionally, as a method to prevent the encapsulant from flowing out and to suppress the width of the encapsulation to a narrower range, there is a known method shown in FIG. 13 of providing a dike-like frame 6a with resin having high viscosity and thus being less likely to flow out around an IC mounted by wire bonding in advance. By this method, the resin 6b has a low viscosity flow within the frame 6a to protect the upper portion, edges, and wire of the IC, and then curing the resin. In case of an IC mounted according to the face-down method, a method basically similar to this is also carried out.
However, a thermal head with a conventional sealing structure as mentioned above has the following problem:    (1) Without a frame, it is difficult to accurately position the edges of the encapsulation due to flowing out of the resin;    (2) It is difficult to accurately position the frame, since the frame for avoiding flowing out of the encapsulant is also made of resin;    (3) If the frame is formed close to the IC for the purpose of reducing the width 8 of the encapsulation, since the frame material has high viscosity, intricate portions of the IC can not be filled with the resin, and therefore, the width 8 of the encapsulation has to be extended outwardly from the IC or the wire by the width 10 of the frame or more.